Regarding the available prior art, reference is made to publications GB-1427818, GB-1429826, DE-2502455 and DE-3641142, which disclose asynchronous electric machine designs that concentrate on so-called squirrel-cage winding designs and particularly on solutions improving the mechanical strength thereof. Efforts have also been made to improve electrical values by traditional optimization, primarily by concentrating on the reduction of eddy-current losses. It should be noted that the above publications concentrate on solutions, where the speeds of rotation are within a relatively low, traditional range of rotating speeds, used for a long time in asynchronous electric machines.
In the design of a conventional, traditional asynchronous electric machine the aim is primarily the optimization of current-heat and magnetization losses, hysteresis losses as well as eddy-current losses. The significance of so-called gas-friction losses is negligible in the design of a traditional asynchronous electric machine.
In general and simplified terms, it can be noted that losses are created in an electric machine and thus also in an asynchronous electric machine as a function of rotating speed as follows: EQU P.sub.h (n)=P.sub.0 +P.sub.1 n+P.sub.2 n.sup.2 +P.sub.3 n.sup.3,(1)
wherein
n=speed of rotation, PA1 P.sub.h =total losses, PA1 P.sub.0 =a standard component, comprising current-heat and magnetization losses, PA1 P.sub.1 =a constant describing hysteresis losses, PA1 P.sub.2 =a constant describing eddy-current losses and other losses associated with the second power of rotating speed, and PA1 P.sub.3 =a constant describing gas-friction losses. PA1 .DELTA.=air gap, and PA1 x=degree of power .gtoreq.0. PA1 P.sub.0 =current-heat and magnetization losses, PA1 .delta.=air-gap, and PA1 y=degree of power .gtoreq.0. PA1 D.sub.s =inner stator diameter (mm), PA1 u=peripheral speed (m/s), PA1 .delta.=air gap (mm), PA1 A=a constant with a magnitude of .gtoreq.0.3, preferably 0.7-1.5, suitably 1; description mm, PA1 B=a constant with a magnitude of .ltoreq.150, preferably 50-100, suitably 70, PA1 C=a constant with a magnitude of .ltoreq.1200, preferably 300-600, suitably 400; description m/s/.sub.mm, PA1 .delta.=air gap [mm], and PA1 P.sub.mek =electric power [kW]. PA1 Q.sub.s =number of stator grooves, PA1 N.sub.u =number of conductors extending in stator groove, PA1 I.sub.1 =the root-mean-square value of a direct wave (A) in stator current, PA1 .delta..sub.1 =the angle between stator current and direct wave of voltage, PA1 A.sub.r =the average cross-sectional area of a rotor coating (section II--II, FIG. 1) (mm.sup.2), PA1 k=load factor (A/mm.sup.2), (fluctuation range 1-2.5), PA1 D.sub.r =numerical value of rotor diameter (mm). PA1 n=rotational speed of electric machine (1/min), PA1 D.sub.r outer rotor diameter (mm), and PA1 .delta..sub.pt =density of coating material (kg/m.sup.3). PA1 D.sub.r =outer rotor diameter/mm. PA1 D.sub.s =inner stator diameter/mm. PA1 n=rotating speed of an electric machine [1/min], and PA1 d.sub.s =filament diameter [mm].
It should be noted in this context that at least all the exponents shown in formula (1) are not in practice integers but, instead, fractions that are close to such figures. Indeed, formula (1) is primarily intended to illustrate interrelations between various types of losses and rotating speed. It should also be noted that constants P.sub.0, P.sub.1, P.sub.2, P.sub.3 adopt varying values depending on relevant, primarily physical factors having an effect on them. In other words, these terms P.sub.0, P.sub.1, P.sub.2, P.sub.3 are only constant relative to rotating speed in a given electric machine construction.
On the other hand, the aim in electric machine design is to minimize the ratio of total losses P.sub.h (n) to shaft output, which is EQU P.sub.aks (n)=k*n, (2)
wherein k=a machine constant, primarily a constant depending on the volume of a rotor and/or an electric machine.
Thus: ##EQU2##
Formula (3) illustrates the effect of increasing the speed of rotation on the relative proportion of losses of the shaft output. An increase of rotational speed reduces the effect of current-heat and magnetization losses (constant P.sub.0). The hysteresis losses are a portion remaining substantially constant. On the other hand, the effect of eddy-current losses (constant P.sub.2) increases substantially in direct proportion to the increase of rotating speed and, furthermore, the effect of gas-friction losses (constant P.sub.3) increases substantially in proportion to the second power of rotating speed.
Hence, formula (3), when of designing an electric machine having high rotating speeds, can be used to draw a conclusion that the effect of constants (P.sub.2 and P.sub.3) associated with eddy-current losses and gas-friction losses should be reduced by effecting such measures in designing that eddy-current losses will be minimized and gas-friction losses shall not at least increase as compared to traditional solutions. On the other hand, the magnitude of constant P.sub.0 associated with current-heat and magnetization losses can even be increased, since the effect of an increase in rotating speed is inversely proportional to the ratio between such losses.